One form of construction of interior walls, partitions, soffits or the like, involves the use of structural framing covered on at least one side by sheets of plasterboard, or dry wall material, butted edge-to-edge. The plasterboard is generally manufactured in standard size sheets, such as four feet by eight feet, or four feet by ten feet, and may be 1/2, 5/8, or 3/4 of an inch in thickness. The plasterboard sheets are cut in-the-field to size; and tape means and a plaster-composition may then be used over the butted joints of the plasterboard sheets, and sanded down to define a smooth finished surface.
For walls, partitions or soffits having two flat sheets of plasterboard meeting one another at an exterior corner, a metal "corner bead" piece is used to cover the exposed edges of the plasterboard sheets, or structural corner as such will hereinafter be termed in this disclosure, to define a solid and true corner edge. The corner bead piece is somewhat L-shaped, having a pair of generally flat legs connected to one another across a slightly rounded exterior corner or bead. The legs are angled relative to one another at just slightly less than 90 degrees, to allow that the piece can be set tightly in place over the exterior structural corner, and have the exposed corner bead set straight and true. Nails may then be driven through holes in the legs of the corner bead piece, through the underlying plasterboard, and into the underlying framing, to secure the corner bead piece in place at, and over, the exterior structural corner.
The tape means and plaster-composition may then also be used over the corner bead piece up the the corner itself, again being sanded down to define smooth finished corner surfaces.
For rapid high-output installation of the corner bead pieces, a crimping tool may be used, instead of nails. One form of crimping tool has an elongated frame comprising two faces angled at right angles across an interior corner that is adapted to be positioned over the corner bead piece, when the latter is itself in place over the exposed edges of the plasterboard sheets. Crimping pins are pivoted to the frame, one relative to each face. Each pin has a die end that, in one rotated position, is recessed behind the face; but in another rotated position, the die end is projected forwardly of the tool face. This basis construction is illustrated in U.S. Pat. No. 2,859,445; where handles connected to the crimping pins are manually shifted to move the die ends against and through the underlying corner bead piece and into the plasterboard, so as to secure the corner bead piece over the exterior structural corner.
Each crimping pin, being pivoted to the tool frame, is rotated almost a quarter turn in one direction as it is being shifted between the recessed and projected positions. The projected die end of each crimping pin moves along a curved path, initially in the direction transverse to the adjacent plasterboard wall, and over the edge of the corner bead piece; and then forwardly toward the structural corner, as it is moving against and deforming the corner bead piece into the plasterboard.
A modified version of that tool provied a striker mounted on a post secured to the frame, the striker being adapted to move toward or away from the back side of the tool faces; and the striker is connected by links to the crimping pins. The striker is adapted to be hit with a mallet to rotate the crimping pins from the recessed positions to the projected positions, rapidly and with a large force, to again move the die ends against and through the underlying corner bead piece.
The link connected between each crimping pin and striker, and the crimping pin itself, cooperate together almost as a toggle linkage. Specifically, when the crimping pin die end is in the recessed position, the crimping pin and link are almost, but not quite, aligned along a straight line; while when the die end is in the projected position, the crimping pin and link are angled sharply, approximately at a right angle, relative to one another. This sharp angular orientation of the crimping pin and link, with this near maximum moment arm, generates a large force on each crimping pin in the latter stages of crimping, as the die end approaches the final projected position.
On the other hand, the near straight line alignment of the crimping pin and link provides a minimum moment arm for the transmission of forces, in converting the impact of the mallet against the striker and the resultant initial movement of the striker toward the structural corner, into effective movement of the die ends toward and into the structural corner. In fact, in order to move each crimping pin from the recessed position toward the projected position, the crimping pin and link each must be rotated, but in opposite directions, and the shaft connection between the two components must be moved laterally of or transverse to the movement of the striker. This linkage effectively transmits only a small portion of the mallet force applied against the striker into rotating the crimping pins, particularly as the linkage is first being moved off of the nearly straight line linkage alignment, but instead is absorbed wastefully by the linkage itself. At times even, the reaction "kicks" the tool frame itself off of the structural corner, and as this can be very large, the operator must exert a considerable manual pushing force against the tool so as to maintain it firmly against the structural corner.
Accordingly, one disadvantage of the impact crimping tool discussed is the high failure rate experienced in the linkage, between the striker and the crimping pins; most commonly, the pivot shaft, between the crimping pin and connecting link, fails. This failure may be caused by the combination of: (1) the quarter-turn rotation of the adjacent components each time the tool is operated, and/or (2) the ineffective transmission of the mallet force striking against the striker. Another disadvantage of the impact crimping tool discussed is the reaction "kick" of the tool frame off of the structural corner; requiring the operator to exert considerable manual pushing force against the tool in order to maintain it against the structural corner.
Still another disadvantage of the impact crimping tool discussed is the inconvenience of having to repeatedly set tne tool, or the mallet, down after use, and then to pick the tool, or the mallet, up when one wants to use it again. This may typically come about when the corner bead piece must be initally located over the structural corner; as it is difficult to simultaneously hold the tool, the mallet, and the corner bead piece, with only two hands; while accurately setting the corner bead piece in place. In this instance, generally the tradesman sets the mallet down, or pinches it between his legs, while using one hand for the tool and the other hand for the corner bead piece. This may be a rather poor solution, for example, if and when the tradesman is standing on a ladder or scaffold, with the typical threat of sway and/or height. During periods of nonuse of the tool, as when the tradesman must measure or cut the corner bead piece to length, or the like, in the attempt to keep the tool on his person, some tradesmen have wired the tool to his tool belt. However, such may not provide stability or comfort of support when the tool is secured onto the tool belt during nonuse; or fast and convenient securement of the tool onto, or removal of the tool from, the tool belt; or durability after repeated use.